The invention relates to a method of bonding a first object, which comprises organic material, to a second object.
Such methods are well known from common experience, and may involve application of an adhesive substance to a surface of at least one of the two objects, subsequent to which this surface is held in contact with a complementary surface of the other object, whereby a chemical bond is formed between the two surfaces. Appropriate adhesive substances for this purpose are manifold, and include pastes, putties, cements, resins and glues, all demonstrating a wide range of chemical, mechanical, thermal, electrical and optical characteristics.
A disadvantage of these known methods is that they result in the permanent presence of a foreign substance (i.e. the adhesive substance) between the bonded surfaces of the two objects. Intended application of the objects in a precision device may thus place stringent demands on the characteristics of the adhesive substance used. For example, if the thermal expansivity of the adhesive substance is not carefully matched to that of the objects to be bonded, then exposure of the bonded objects to large or sudden changes in temperature may result in partial or complete severance of their bonded surfaces, due to the mechanical stresses arising from differential thermal expansion. Alternatively, application of the bonded objects in an ultra-high vacuum environment will necessitate use of an adhesive substance having a sufficiently low vapour pressure, so as to minimise outgassing. Furthermore, in applications requiring highly accurate mutual positioning of the two objects, such as the manufacture of integrated circuits or precision optics, allowances must be made for the thickness of the interfacial adhesive substance itself, especially since this will usually be inhomogeneous.
These considerations often necessitate the development of special adhesive substances for particular applications, at high cost. Such adhesive substances are often toxic and inflammable, so that care must be exercised both in their application and in their disposal. Moreover, many such adhesive substances contain solvents which can seriously degrade the surfaces of organic materials.
A further disadvantage of the known-methods is that they often do not provide an instant bond between the two objects. Rather, the objects must be held in motionless contact for an extended interval of time, so as to allow sufficient setting of the adhesive substance and consequent formation of an interfacial chemical bond between the objects. This extended interval of time may last up to several hours, and hinders bonding of the objects by rapid, continuous mass-production techniques. Furthermore, application of an adhesive substance in a production process requires special precautionary measures to avoid contamination of products and machinery by that substance.